In recent years, global scale environmental destruction problems such as global warming, ozone layer depletion, acid rain, etc. have gained prominent attention. Internationally, environmental pollution measures are advocated, and various regulations have been established from the viewpoint of environmental protection. Among them, release into the atmosphere of organic solvents (VOC) has been a serious problem, and also in each industry, the movement for de-organic solvents (de-VOC) along with the trend for strengthening VOC regulations has become active. Also in the paint industry, as a substitute for conventional organic solvent-based coating material, a powder coating material is highly expected as a coating material which contains no VOC and which is friendly to the environment as it can be recovered and reused without requiring exhaust treatment or wastewater treatment.
As such a powder coating material, an acrylic resin powder coating material, a polyester resin powder coating material or an epoxy resin powder coating material, is mainly used.
However, cured films formed by using these powder coating materials have such a drawback that they are poor in weather resistance.
As a powder coating material to overcome such a drawback, a hybrid powder coating material has been proposed, wherein a powder containing a polyester resin and a powder containing a fluororesin are dry-blended (see e.g. Patent Documents 1 to 3).
Using such a hybrid powder coating material, it is possible to form, by one coating, a cured film having a double-layered structure comprising a cured resin layer made of the polyester resin on the substrate side and a fluororesin layer on the air side. Such a cured film is excellent in weather resistance, since it has a fluororesin layer on the air side.